The Genus Microcystis in Ceylon 63 
This species differs from M. flos-aquce and M. ceruginosa in its 
more irregular colonies and especially in the predominantly dis¬ 
sociated state of the cells. As some transitional forms of this species 
closely approach M. flos-aquce it was at first regarded as a form of 
the latter species. Thus in colonies from Perithpan-pokuna much of 
the material was comparatively well provided with mucilage, the 
distances between adjacent cells being about 2-4 times the cell- 
diameter. In tank Mineri and a pool near tank Punchi-kekirawa 
typical specimens occurred in association with colonies of the form 
of typical M. flos-aquce. As, however, very large numbers of loose 
colonies in the dissociated state shown in Fig. d have been observed 
in material which shows evidence of normal conditions both of growth 
and preservation, there can be no doubt that M. protocystis forms 
a distinct type. The difference between this and any previously 
known species is as great as any specific distinction within the genus. 
In Wesenburg-Lund’s ( 9 ) description of M. flos-aquce and its forms, 
he mentions nothing approaching the dissociated condition of M. 
protocystis. The latter must on our present knowledge be considered 
as a perfectly independent species. The presence of transitional forms 
resembling those of M. flos-aquce suggests that further investigation 
may show such forms to be a regular phase in the life-history of 
M. protocystis, but should this prove to be the case it would not be 
sufficient to show the latter to be identical with typical M. flos-aquce . 
M. protocystis naturally extends the range of variation known in 
the genus Microcystis. In fact it falls within the generic definition 
of Aphanocapsa as given by some authors. But to place it in the latter 
genus would be to obscure its natural affinities. The great distance 
apart of the cells and the quite indefinite colonies are of course 
features wholly in accord with Aphanocapsa. It must be noted, 
however, that these two characters by no means exclude it from the 
genus Microcystis. The present writer has shown in a previous pub¬ 
lication (l) that the distance apart of the cells is one of the least 
important specific characters in the species of Microcystis. It is well 
known, too, that the definite character of the colony is by no means 
equally maintained in the species (see e.g. figures given here). It 
might, of course, be supposed that these characters (i.e. wide dispersal 
of the cells, indefinite nature of the colony) were so well developed 
in M. protocystis that it might be regarded as having passed beyond 
the limits of the genus Microcystis, not because there is any great 
gap between this species and the related members of Microcystis but 
because in it the characters referred to seem to reach their highest 
